In offset printing, when printing machines are utilized having non-integrated ink and dampening liquid systems, it is typical to provide a plurality of ink roller devices that interact to transfer ink from an ink reservoir to a rotating photographic printing plate and it is also typical to provide a dampening liquid supply system that applies dampening liquid to the printing plate. The dampening liquid supply system typically incorporates a plurality of inter-engaging rollers that transfer a dampening liquid to the photographic printing plate. The dampening liquid serves to coat the photographic printing plate with a precise quantity of the dampening liquid or solution that causes ink to be repelled only on those portions of the printing plate that have not been specifically prepared to receive the ink. With the ink deposited on the specific portions of the printing plate, paper stock is fed from a paper supply through the printing machine where it comes into contact with the blanket of a blanket roll, which blanket receives the image to be printed from the rotating printing plate. Transfer of the ink is accomplished from the specifically prepared portions of the printing plate to the blanket roll and then to the paper or other sheet stock to be printed.
It is also typical to provide a fountain roller having a portion thereof located within a fountain reservoir that contains a quantity of dampening liquid with the quantity of liquid within the fountain reservoir remaining essentially constant. The fountain roller is typically formed of aluminum and will typically have a smooth outer periphery. A ductor roller is supported by the framework of the machine not only for rotation but also for transverse movement. The ductor roller comes into contact with the fountain roller at one extremity of its lateral travel and at the other extremity of its travel comes into contact with the outer surface of a rider roller. The ductor roller and the rider roller are typically formed of a soft rubberlike material such as synthetic rubber having a hardness of approximately thirty durometer. A form roller is maintained in co-rotating engagement with the rider roller and also with the photographic printing plate carried by the rotating plate cylinder. The form roller is typically composed of the same soft rubberlike material as the ductor and rider rollers, but is typically provided with a dampening roller sleeve that has the capability of retaining a large quantity of dampening liquid in order to provide for proper distribution of dampening liquid to the photographic printing plate.
Dampening system rollers of offset printing machines are typically composed of solid metal while the ductor roller adjacent thereto is typically formed of soft material with a cloth covering applied thereto to assist in retention and distribution of the dampening liquid. The oscillator roller is typically composed of aluminum and the form roller, also frequently referred to as the dampening roller of the dampening system, is a soft roller that is covered with a dampening liquid retaining sleeve. One type of liquid retaining sleeve is referred to as the Molleton cover, which is formed of a fabric material that retains the dampening liquid but, when wet or damp, is very slow to attract ink. Molleton covers come in many varieties and may be purchased ready cut for the form rollers of printing presses in tubular or wraparound strip form, or in continuous rolls of tubular material. Some of the sleeves incorporate an elastic material that retains the sleeve in assembly with the roller and in other cases, the sleeves are provided with tying strings that are used to tighten the sleeves on the rollers. Although a greater quantity of Molleton covers are utilized in offset printing presses than other dampening devices, other liquid retaining covers, such as fiber covers are also employed which serve to retain a quantity of dampening liquid for the purpose of coating the printing plate as it rotates in contact with the dampening form roller.
One of the major problems with Molleton covers, which problem is eliminated to some extent by fiber covers, is the fact that the Molleton sleeve, being composed of a fabric material, will bulge to some extent in the area of contact with the rider roller and with the rotating photographic plate. Bulging of the fabric material can cause the photographic plate to be smeared to some extent and this causes the image printed to be less than sharp and precise. The fiber covers are typically not subject to excessive bulging and, when utilized with a matching sized dampening roller, insure fairly good printing performance. Because of the difficulty of installing and caring for fiber covers for dampening rollers, Molleton covers are much more widely utilized in the printing industry at the present time.
Another problem encountered when utilizing Molleton covers for dampening form rollers of offset printing presses is the problem caused by lint that comes off of the dampening form roller during the printing process. Loose lint can cause inaccuracies in the printing process and can result in a large amount of wasted paper stock and ink waste in order to provide a customer with quality printing work.
The fabric or cloth material of the Molleton covers, as well as the softness of the fiber covers that are presently utilized in the dampening systems of offset printing presses, will not typically allow printing work to be as sharp and precise as might otherwise be desirable. The dampening covers, because of their need to retain a quantity of dampening liquid for efficient coating of the rotating photographic printing plate will, because they are composed of soft fabric or fibrous material, cause some smudging of the plate which prevents the linework being printed from being as sharp and clear as might otherwise be desirable. Moreover, when printing large areas of solid black, the Molleton and fiber covers provide limitations to the particular size of the area that can be printed. For example, when printing solid black areas, efficient printing can be obtained when the size of the area being printed is restricted to approximately three inches or so. As will be explained herein below, the present invention effectively provides a printing technique whereby solid black areas in the order of six inches may be efficiently printed without any sacrifice whatsoever from the standpoint of clarity and accuracy.
Another major problem encountered when utilizing Molleton covers and also encountered to a certain extent when utilizing dampening roller covers composed of synthetic fiber, is the amount of "run in" time that is necessary to cause the dampening liquid content of the dampening roller sleeve to be optimum for accurate printing. To insure that dampening covers and photographic printing plates do not pick up a quantity of ink when the printing press is initiated with improperly moistened covers, it is typically the practice in the industry either to initially moisten the covers by hand or, which is more preferred, to run the printing machine for approximately fifteen minutes or so to allow the dampening system of the machine to achieve the right moisture content. Where the dampening covers are moistened by hand, it is very easy for the covers to become excessively wet. When this occurs, it is necessary either to allow the machine to remain idle for an hour or two to allow the covers to loose some of the moisture or to run a quantity of paper through the machine to allow the paper to absorb the excessive moisture. It is not unusual for an operator to run 200 sheets of paper through the machine before the moisture content of the dampening roller covers reaches the level for optimum printing. This of course is wasteful, not only because of the paper that is wasted, but also because of losses caused by down-time on the machine. It is of course desirable to limit the amount of downtime and the amount of run in time that is necessary to produce optimum printing impressions.
It is also desirable to reduce as much as possible the number of printing copies that are made before the printing machine is properly adjusted to produce quality prints. In the past, using Molleton covers and fiber covers, a large number of copies were necessary before the ink and moisture content applied to the printing plate could reach an optimum level. It is not unusual for an operator to run from 100 to 200 printing sheets before quality printing is achieved. This is undesirable from the standpoint of paper waste as well as waste of machine and employee printing time. As will be explained in detail hereinbelow, the present invention effectively promotes very low waste of paper and employee printing time to achieve optimum printing when a printing run is initiated. For example, efficient printing may be accomplished after approximately five sheets of paper have been run, because of the simplicity of machine adjustment that is achieved by utilizing the dampening roller system of the present invention. In addition, the run in time for initiating a printing operation can be very low or practically non-existent when the present invention is utilized in connection with offset printing presses having non-integrated dampening liquid and ink systems. In accordance with the context of the present invention, the term "non-integrated system" or "non-integrated ink/dampening liquid system" is intended to refer to those types of offset printing machines that accomplish printing with the supply of ink and the supply of dampening liquid being maintained separately and applied separately to the rotating photographic printing plate. By the term "integrated system" those offset printing machines that are referred to incorporate ink and dampening liquid systems, whereby the ink and dampening liquid are placed onto the photographic printing plate simultaneously. The present invention functions efficiently and produces novel results when utilized in context with non-integrated systems, but does not apply to integrated systems.
Offset printing presses are widely utilized to accomplish multi-colored printing. When this is done, the paper being printed is processed through the printing machine once for each of the particular colors being printed if the printing machine has only a single plate cylinder. Because of the likelihood that Molleton covers and fiber covers for the rotating dampening form rollers will pick up a quantity of ink during any particular printing process, it is virtually necessary that the covers be changed between each of the colors being printed. This, of course, causes excessive machine downtime and is also quite expensive because the Molleton covers frequently have a cost in the order of five dollars each. It is therefore desirable to provide an efficient dampening system that can be quickly cleaned in order to provide for printing of different colors without necessitating change of the covers of the dampening rollers between the printing of each color.
It is therefore a primary feature of the present invention to provide a novel dampening system for offset printing presses whereby Molleton and fiber covers for the dampening rollers are eliminated, thereby also eliminating the cost in the form of purchasing, installation, removal, cleaning and breaking in of the Molleton covers.
It is a further feature of the present invention to provide a novel dampening system for offset printing presses that effectively allows run in time and preliminary paper runs to be maintained as low as possible to achieve efficient productive printing.
It is also an important feature of the present invention to provide a novel dampening system for offset printing presses when problems of printing inaccuracy caused by lint or caused by smudging contact between soft fabric or fiber dampening covers and photographic plate are effectively eliminated.
Among the several features of the present invention is noted the contemplation of a novel dampening system for offset printing presses whereby extremely sharp and precise printing is accomplished through the use of offset printing presses having non-integrated systems.
It is also a feature of the present invention to provide a novel dampening system for offset printing presses whereby presently existing offset printing presses having non-integrated ink and dampening liquid systems can be efficiently modified in a few minutes time to convert the same to accomplish printing within the spirit and scope of the present invention.
It is also a feature of the present invention to provide a novel printing process for offset printing presses having non-integrated ink and dampening liquid systems whereby soft, rubber, smooth surfaces ductor and form rollers are employed, with a hard and smooth non-metal roller provided therebetween and for contact therewith to accomplish efficient metering of dampening liquid to the photographic printing plate and applying and dampening liquid to the photographic printing plate in such a manner that no smudging takes place and the images printed are therefore sharp, precise and free from the distortion that is typically caused by Molleton or fabric covers.
Other and further objects, advantages and features of the present invention will become apparent to one skilled in the art upon full consideration of the present disclosure. The form of the invention, which will now be described in detail, illustrates the general principals of the invention, but it is to be understood that this detailed description is not to be taken as limiting the scope of the present invention.